A washing machine appliance can use a variety of fluids (in addition to water) to wash and rinse laundry and other articles. For example, laundry detergents and/or stain removers may be added during wash and prewash cycles. Fabric softeners may be added during the rinse cycles.
These fluid additives must be introduced at an appropriate time during the cleaning process and in a proper amount. By way of example, adding laundry detergent and fabric softener at the same time into the water used for a laundry load is undesirable because the resulting mixture is unlikely to clean or soften as the two will negate each other. Not adding enough of either the detergent or softener to the laundry load will diminish the efficacy of the cleaning process. Conversely, adding too much detergent or softener is also undesirable.
For instance, when too much detergent is added during a wash cycle, this can leave some detergent that remains on the clothes because the rinse cycle of a washing machine may not be able to remove all of the detergent used during the wash cycle. In turn, this can lead to a graying effect on the clothes as the detergent builds up over time, can contribute to a roughness feeling, and potentially may even affect skin allergies. The excess detergent can also negatively affect the efficacy of the fabric softener during the rinse cycle. Excess detergent can also cause excess suds which may be undesirably left on the clothes after a wash cycle, cause damage to the washing machine, and/or cause the spin speed to decrease therefore causing the clothes to retain too much water.
As a convenience to the consumer, systems for automatically dispensing detergent and/or fabric softener can be provided. Such automatic systems can store one or more fluid additives in bulk and dispense at the appropriate times during a wash cycle. Challenges are still encountered, however, in metering the appropriate amount of the fluid into a wash or rinse cycle with such automatic systems.
For example, while a pump—such as a peristaltic pump—can be used to meter the fluid additives in reasonably accurate quantities, such adds a significant cost to the manufacture of an appliance. Additionally, a control system must be provided to properly operate the pump during the various cycles of the appliance. Less expensive pumping devices, such as an aspirator as indicated in e.g., in U.S. Pat. No. 2,712,747, may be used. However, these alternatives also present certain challenges. By way of example, where an aspirator is utilized, a fluid such as water can be passed through the aspirator to pull a fluid additive from a bulk dispenser and deliver the same to another part of the appliance such as a wash tub. The amount of fluid dispensed in such manner is determined in part by the velocity of water through the aspirator.
Unfortunately, the pressure available from the user or consumer's water supply can vary substantially. Not only can the water pressure vary from consumer to consumer, but significant pressure variations can also occur at a particular user's location depending upon e.g., simultaneous water usage for bathing and/or by other appliances, etc. These variations can significantly impact the dosage of fluid additive where a pumping device such as an aspirator is utilized because the suction available to pull fluid additive from a bulk dispense container will vary with changes in the water pressure provided to the aspirator.
Additionally, different fluid additives may have different densities and/or viscosities that can significantly affect the flow characteristics. As such, simply using a predetermined pumping time to deliver a fluid additive into e.g., the wash tub of the appliance can lead to undesirable variations and incorrect quantities in the amount of fluid additive delivered where substantial changes in viscosity and/or density occur between different fluid additives that may be used in the appliance.
Thus, a system for metering a fluid in an appliance would be useful. More particularly, a system that can enhance the delivery of accurate amounts of fluid additive during a wash or rinse cycle of an appliance would be beneficial. Such a system that can make adjustments for differences in the water pressure available to the appliance and/or differences in density or viscosity of the fluid additives would be particularly useful.